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Nature 449, 517 (4 October 2007) | doi:10.1038/449517a; Published online 3 October 2007

Water doesn't mind the gap

Eric Hand

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Gravity-defying liquid bridge makes a splash.

Water doesn't mind the gap

E. FUCHS/ GRAZ UNIV. TECH.

Researchers have managed to create a bridge of water between two beakers.

It could be the world's longest liquid bridge: researchers have coaxed water into leaping a 25-millimetre gap between two regular glass beakers in a gravity-defying stunt. The engineering feat could involve a hitherto unknown microstructure of water, the researchers say.

?Nobody would expect stable bridges to form,? says Elmar Fuchs, a physical chemist at Graz University of Technology in Austria.

Fuchs's team applied up to 25,000 volts across electrodes placed in two beakers filled nearly to the brim with distilled water. Within a millisecond, water crawled up to the edge of one beaker and, in a burst of sparks, leapt across the gap between them. As the researchers moved the beakers apart, the bridge grew. The resulting thin cylinder of water stood for up to 45 minutes (E. C. Fuchs et al. _J. Phys. D_ 40, 6112?6114 ; 2007).

?The bridging part is new ? I haven't seen that,? says Hsueh-Chia Chang, a chemical engineer at the University of Notre Dame in Indiana. However, he says, the achievement is ?not that surprising?.

Chang uses electric fields to expel water droplets from the tips of capillaries in cone-shaped jets called electrosprays. He says that the water bridge relies on similar phenomena, on a bigger scale. The bridge takes advantage of the well-understood polarity of water molecules ? due to the positively charged hydrogens and the negative oxygen. In an electric field, water molecules line up. In this case, Chang theorizes, the molecules orient themselves to form a cylindrical bridge. The repulsion between similarly charged atoms effectively wedges the bridge in place, he suggests.

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Using a charged glass wand, Fuchs and his colleagues could bend the bridge from side to side. They found that water actually flowed through the centre of the bridge, from one beaker to another. The team analysed the moving water and found that it was denser than the surrounding bridge. Fuchs says he doesn't fully understand the phenomenon, but speculates that the denser water coalesces into microstructures that somehow strengthen the bridge. The group plans to carry out X-ray experiments to determine the molecular structure of the water flowing through the bridge.

The bridge lasted until too many dust particles and ions had entered the water, increasing the current across the bridge. It heated up and eventually ruptured.